[tracing] Re-enable mmaps dump provider for memory-infra
[tracing] Re-enable mmaps dump provider for memory-infra

As agreed during the offline meeting, it is OK for chrome://tracing
to get mmaps dumps into the trace data, as long as the infobar
indicating that an extension with the debugger permission is
using the devtools protocol is showed on all tabs.
The latter happened in crrev.com/1295493005 (see crbug.com/521686),
so this is effectively a revert of crrev.com/1275013005.

BUG=517906

Review URL: https://codereview.chromium.org/1311163004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#347201}

CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend